This relates generally to imaging devices, and more particularly, to imaging devices with improved backside illumination (BSI) compatible global shutter pixels that do are less sensitive to imperfect light shielding.
Modern electronic devices such as cellular telephones, cameras, and computers often use digital image sensors. Image sensors (sometimes referred to as imagers) may be formed from a two-dimensional array of image sensing pixels. Each pixel includes a photosensitive region that receives incident photons (light) and converts the photons into electrical signals. Image sensors are sometimes designed to provide images to electronic devices using a Joint Photographic Experts Group (JPEG) format.
Image sensors may sense light by converting impinging photons into electrons or holes that are integrated (collected) in sensor pixels. After completion of an integration cycle, collected charge is converted into a voltage, which is then supplied to the output terminals of the sensor. After charge to voltage conversion is completed and the resulting signal transferred out from the pixels, the pixels may be reset in order to be ready for accumulation of new charge.
Some conventional image sensors use a global shutter method to read out signals from all pixels in the image sensor simultaneously. These global shutter pixels are susceptible to kTC noise, and can experience undesirable interference from incident light when used in BSI image sensors.
It would therefore be desirable to be able to provide imaging devices with improved global shutter pixels that are compatible with BSI image sensors.
Some conventional image sensors use a global shutter method that involve storing signal charges on capacitors in the voltage domain. These global shutter pixels require large capacitors to store both RESET and SIGNAL values, as described in, for example, U.S. Pat. No. 8,569,671, entitled “Pixel Array Capable of Performing Pipelined Global Shutter Operation Including a First and Second Buffer Amplifier.” Unfortunately, these capacitors take up an undesirably large amount of space on the image sensor.
It would therefore be desirable to be able to provide imaging devices with global shutter pixels that require fewer or smaller capacitors.